Magnetic tapes, unlike movie film cannot be suitably edited by cutting and splicing. As a practical matter, magnetic tapes of all types are edited by making a new edited tape from one or more source tapes on which the original recording has been done. Considering a typical video tape problem, in producing a television drama, for example, it may be more convenient to record scenes out of order of the sequence in which they will appear on television. For example, if scenes 2 and 5 are taken in one setting it may be of advantage to take scene 2 and then immediately take scene 5, later recording, out of sequence, scenes 3 and 4. When this is done, the editing process will interpose scenes 3 and 4 between scenes 2 and 5. Editing requires knowing or being able to determine precisely where one scene ends and the next scene begins on the tape. In making the edited tape, for example, after transferring scene 2 to the edited tape, the edit tape deck is stopped precisely at the end of scene 2. This can be done by visually observing the picture produced on the monitor from the source tape at the time it is being edited and transferred to the edited tape. Then while the edit tape deck is stopped, the source tape used in taking the scenes must be rolled ahead to the point where scene 3 begins. When scene 3 is found, it is not possible to simply start up the edit tape deck and start recording. In order to get a proper recording a tape deck must be up to speed before recording starts. This requires back-spacing both the edit and source tapes before recording to allow each tape to accelerate to recording speed so that recording can begin the proper place.
As a practical matter, in the prior art, editing was done as a matter of guess work with the editor making his best judgement about how far to backup each tape deck and then trying to synchronize the source and edit tape decks so that the edit points occur at the same time. Editors have had to guess and either took long periods on the average or produced edited products of variable quality. Others have used various aids such as measuring the tape and marking a starting place physically with markers, or ink, but this is tedious, time consuming and subject to error.